Mycothiol (MSH) is a small molecular weight biomolecule used to modify drugs in the Actinobacteria phylum. Mycobacterium tuberculosis (Mtb) produces the greatest intracellular concentrations of this unique thiol-containing biomolecule. Interest regarding MSH biosynthesis in Mtb is due to its importance in redox homeostasis in the bacterium as well as the role of mycothiol in neutralizing antibiotics used to treat Mtb infections. The mycothiol S-transferase (MST) enzyme that catalyzes the conjugation of MSH to a variety of compounds has been identified. Considering the prominent role of mycothiol in Mtb drug metabolism, a deeper understanding of the structure and function of MST will lead to a clearer understanding of this important defense mechanism that promotes antibiotic resistance in Mtb.